For the average person, up to 300 mg of coffee a day, or two to four cups of the average brewed coffee, is a moderate amount that isn't harmful. But once you hit more than four cups, you may experience less-than-desirable side effects. Drinking more than 500 mg every day, in fact, can induce anxiety, insomnia, and muscle tremors and can even lead to increased heart rate and blood pressure, headaches, or digestion issues.

If you want to stay away from the caffeine jitters, then limiting yourself to under four cups of coffee per day is a perfectly reasonable plan. However, you may be surprised by how much caffeine is in your favorite caffeinated beverage; it can be much more than you think!

Use this chart as a guide to see how much caffeine you're really consuming every day. Even if you enjoy two eight-ounce cups at Starbucks, for example, that's 360 mg of caffeine — 60 mg over the recommended limit.

Also, remember that even though espresso-based drinks like lattes and cappuccinos contain less caffeine than brewed coffee, many drinks are made with at least two espresso shots, not one.